1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a piezoelectric radio frequency (RF) micro electro mechanical system (MEMS) device and a method of fabricating the same, and, more particularly, to a piezoelectric RF MEMS device and a method of fabricating the same, in which a piezoelectric actuator is provided with an RF input signal line for one point contact at a low voltage and the RF MEMS device is fabricated as one package.
2. Description of the Related Art
An RF MEMS device is used as a multi-function switch, a relay, a capacitor or a phase shifter in various fields such as radar, mobile and communication products. Examples of the RF MEMS device include an electrostatic RF MEMS device based on electrostatic phenomenon and a piezoelectric RF MEMS device based on a piezoelectric effect. However, the electrostatic RF MEMS device requires a high driving voltage of 3V and has a large volume. In this respect, the piezoelectric RF MEMS device is being widely used.
FIG. 1 illustrates a piezoelectric RF MEMS switch which is one of related art RF MEMS devices. FIG. 1A is a plane view illustrating the piezoelectric RF MEMS switch, FIG. 1B is a sectional view taken along line A-A of FIG. 1A, and FIG. 1C is a plane view illustrating a lower substrate of the piezoelectric RF MEMS switch. The piezoelectric RF MEMS switch 1 is disclosed in the Korean Patent Laid-Open Publication No. 10-2005-0076149. As shown in FIGS. 1A to 1C, the piezoelectric RF MEMS switch 1 includes an upper substrate 10, a lower substrate 20 provided with RF input and output signal lines 21 and 22, a piezoelectric actuator 30 whose one end is fixed to the upper substrate 10 and other end is spaced apart from the lower substrate 20, and a contact pad 34 arranged on an end of the piezoelectric actuator 30. The piezoelectric actuator 30 is formed below the upper substrate 10, and has a structure that a piezoelectric layer 33 such as lead zirconate titanate (PZT, Pb(Zr,Ti)O3) is interposed between an upper electrode 31 and a lower electrode 32. An elastic layer 12 is formed between the upper substrate 10 and the upper electrode 31. The upper substrate 10 is a semiconductor wafer substrate, and the end of the piezoelectric actuator 30 is positioned in a trench area 13 of the upper substrate 13. The lower substrate 20 is provided with a coplanar waveguide (CPW) lines such as bumps 23 and 24 in addition to the RF input and output signal lines 21 and 22.
Unlike the electrostatic RF MEMS switch, the aforementioned piezoelectric RF MEMS switch 1 can be driven at a low voltage. Also, the piezoelectric RF MEMS switch 1 is relatively smaller than the electrostatic RF MEMS switch, and has a switching speed faster than that of the electrostatic RF MEMS switch. In the piezoelectric RF MEMS switch 1, if an external voltage is applied to the upper and lower electrodes 31 and 32 of the piezoelectric actuator 30 through the bumps 23 and 24 of the lower substrate 20, moment occurs in the piezoelectric layer 33 to down bend the piezoelectric actuator 30, and the contact pad 34 contacts the RF input and output signal lines 21 and 22 to transmit an RF signal to an RF circuit board, i.e., the lower substrate 20. However, in the piezoelectric RF MEMS switch 1, the contact pad 34 of the piezoelectric actuator 30 contacts the RF signal lines 21 and 22 at two points. This two-point contact manner deteriorates stability of the switching operation in comparison with one point contact manner.